Neurological disorders are often caused by neural impulses failing to reach their natural destination in otherwise functional body systems. Local nerves and muscles may function, but, for various reasons, such as injury, stroke, or other cause, the stimulating nerve signals do not reach their natural destination. For example, paraplegics and quadraplegics have intact nerves and muscles and only lack the brain to nerve link, which stimulates the muscles into action.
Prosthetic devices have been used for some time to provide electrical stimulation to excite muscle, nerve or other cells. Such devices have ranged in size and complexity from large, bulky systems feeding electrical pulses by conductors extending through the skin, to implanted stimulators which are controlled through high-frequency, telemetry signals, which are modulated rf signals, such as set forth in U.S. Pat. No. 4,524,774, Apparatus and Method for the Stimulation of a Human Muscle, invented by Jurges Hildebrandt, issued Jun. 25, 1985. The use of frequencies of 27.12 MHz and 40.6867 MHz are there mentioned. Other devices have comprised a centrally-implanted stimulator package sending stimulation signals to a multitude of distant target sites.
Complications, including the possibility of infection, arise in the use of stimulators which have conductors extending through the skin. On the other hand, in the use of implanted stimulators, difficulties arise in providing suitable, operable stimulators which are small in size and in passing sufficient energy and control information to the stimulators, without direct connection, to satisfactorily operate them without direct connection.
The device of the invention uses a source of electrical energy, modulated by desired control information, to selectively control and drive numerous, small stimulators disposed at various locations within the body. Thus, for example, a desired, progressive muscular stimulation may be achieved through the successive or simultaneous stimulation of numerous stimulators, directed by a single source of information and energy outside the body.
The appropriate, functioning design of a suitable, small stimulator, a microstimulator, which can be easily implanted, such as by expulsion through a hypodermic needle, is difficult to achieve. Notwithstanding the small size, the microstimulator must be capable of receiving and storing sufficient energy to provide the desired stimulating pulses, but also, may be required to respond to received control information as to pulse duration, current amplitude and shape. Further, stimulators should achieve a "charge balancing", that is, a balancing of current flow through the body tissue in both directions to prevent damage to the tissue which results from continued, preponderance of current flow in one direction.
Also in providing the "charge balancing", it must be assured that the current flow in the opposite direction from the stimulation pulse does not cause damage to the intermediate body cells or cause undesired stimulation. Further, the "charge balancing" must not cause anodic or cathodic deterioration of the stimulating electrodes.